Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
  • H01J37/32—Gas-filled discharge tubes
  • H01J37/32009—Arrangements for generation of plasma specially adapted for examination or treatment of objects, e.g. plasma sources
  • H01J37/32082—Radio frequency generated discharge
  • H01J37/32091—Radio frequency generated discharge the radio frequency energy being capacitively coupled to the plasma
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
  • H01J37/32—Gas-filled discharge tubes
  • H01J37/32009—Arrangements for generation of plasma specially adapted for examination or treatment of objects, e.g. plasma sources
  • H01J37/32082—Radio frequency generated discharge
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
  • H01J37/32—Gas-filled discharge tubes
  • H01J37/32009—Arrangements for generation of plasma specially adapted for examination or treatment of objects, e.g. plasma sources
  • H01J37/32082—Radio frequency generated discharge
  • H01J37/32174—Circuits specially adapted for controlling the RF discharge
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
  • H01J37/32—Gas-filled discharge tubes
  • H01J37/32009—Arrangements for generation of plasma specially adapted for examination or treatment of objects, e.g. plasma sources
  • H01J37/32082—Radio frequency generated discharge
  • H01J37/32174—Circuits specially adapted for controlling the RF discharge
  • H01J37/32183—Matching circuits
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
  • H05H1/00—Generating plasma; Handling plasma
  • H05H1/24—Generating plasma
  • H05H1/46—Generating plasma using applied electromagnetic fields, e.g. high frequency or microwave energy

Definitions

• the present invention relates in general to RF capacitive coupled plasma reactors for processing a very large area display. More specifically, the present invention relates to improvements in the coupling efficiency of the RF power delivered to plasma typically at a frequency of 13.56MHz or less.
• the present invention is based on problems and requirements that have arisen in depositing semi-conductive layers on very large glass areas for the display and solar manufacturing industries.
• the resulting solution can be applied to other applications.
• the present invention will be described relating to plasma reactors for Plasma Enhanced Chemical Vapor Deposition (PECVD) systems for very large area display processing, the present invention can also be applied to other applications relating to plasma reactors. Further, the development of PECVD for very large area display processing is disclosed in U.S. Pat. No. 6,281,469, the contents of which are herein incorporated by reference.
• FIGURE 1 shows a conventional capacitively-coupled, RF-plasma reactor system 10 for a PECVD system.
• the reactor system 10 includes an RF power supply 12, a matching network 14, a reactor chamber 16, and a vacuum chamber 18.
• the reactor chamber 16 includes two metallic plates 20, 22 arranged in parallel enclosed in a metallic-reactor casing 24.
• the first metallic plate 22 is electrically connected to the RF power supply 12 via a feeding element 26 and the matching network 14 and the first metallic plate 22 is, thus, a live electrode.
• the second metallic plate 20 is connected to ground and is, thus, a ground electrode. During the deposition process a substrate is placed on the second metallic plate 20
• the feeding element 26 is shielded with a grounding shield 28 and can be any type of electrical feeding element known in the ait, such as an RF stripline, RF ribbon, or a triplate stripline.
• a plasma-discharge region 30 is defined in between the two metallic plates 20, 22.
• the RF power supply 12 and matching network 14 are located outside the vacuum chamber 18 and the reactor chamber 16 and feeding element 26 are located inside the vacuum chamber 18.
• the RF power supply 12 and the matching network 14 are under atmospheric conditions and the reactor chamber 16 and RF feed line 28 are under vacuum conditions.
• a typical gas used for forming a plasma in the PECVD process is a silicon nitride SiN gas. Other gases commonly known in the art, however, may be used in this type of application such as organometallics, hydrides and halides.
• FIGURE 2 shows a simplified equivalent circuit of the conventional PECVD system during the deposition of SiN and will be used to illustrate the disadvantage of the conventional RF-plasma reactor system 10.
• the dotted line boxes represent a portion of the conventional RF-plasma reactor system 10 as indicated by the reference numbers.
• a disadvantage to this process in large area parallel plate reactors is that a very large parasitic-reactor capacitance C R , typically greater than 500OpF, forms between the live electrode 22 and the grounded reactor casing 24.
• the feeding element 26 must be capable of handling very large RF currents I F , typically greater than 300A.
• the large RF currents require a very wide stripline design, which leads to a second parasitic-feed-line capacitance C F between the live wire of the feeding element 26 and the grounding shield 28.
• the feed-line capacitance Cp is typically greater than 300OpF.
• the reactor C R and feed-line Cp capacitance transform a plasma impedance Zp to a feed-through impedance Re(Zp) having a very small value, typically less than 0.05 ohms.
• the feed-through impedance Re(Zp) is the impedance as seen at the entrance of the vacuum chamber 18 where the feeding element 26 enters the vacuum chamber 18.
• the feed-through impedance Re(Zp) in turn creates a larger RF current Ip, typically greater than 400A, which now must be accommodated by the matching network 14 and the feeding element 26.
• Ip typically greater than 400A
• the efficiency of the system is low, typically ⁇ s ⁇ 0.3. Therefore, very large and expensive RF power supplies are required in order to achieve the necessary plasma power density and deposition rate. Further, as the size of the glass increases the efficiency of the plasma power coupling efficiency decreases to values less than 20% at an RF frequency of 13.56MHz.
• the parasitic capacitance C R and C F could be reduced by increasing the gap between the live parts, i.e. the live electrode 22 and feeding element 26, and the grounded parts, i.e. the reactor casing 24 and the ground shield 28.
• the disadvantage to this solution is that the plasma between the gaps could ignite.
• Another solution is to water cool the reactor. This, however, is difficult in a vacuum system and water cooling does not significantly enhance the plasma coupling efficiency.
• Another solution is adding an impedance-transformation circuit to the RF-plasma reactor system 10. Power losses through the lossy elements RM, R F in the matching network 14 and the feeding element 26 respectively can be reduced by decreasing the RF current I F . Reducing the RF current Ip while maintaining the plasma power can be accomplished with an impedance-transformation circuit, which increases the feed-through impedance Re(Zp).
• an impedance-transformation circuit solely made of one inductor is impractical for several reasons. For example, the inductor needs to be a low- loss inductor, there is nothing to prevent the DC voltage from shorting to ground, and there is no tuning capability.
• a plasma reactor comprising, a vacuum chamber, a first metallic plate and a second metallic plate located inside the vacuum chamber, an RF power supply, a matching network, a plasma-discharge region containing plasma defined between the first and second metallic plates, a feeding element electrically connected to the first metallic plate, and an impedance-transformation circuit electrically connected to the first metallic plate.
• a plasma reactor comprising, a vacuum chamber, an RF power supply, a matching network, a first metallic plate and a second metallic plate located inside the vacuum chamber, a plasma-discharge region for containing plasma defined between the first and second metallic plates, a feeding element electrically connected to the first metallic plate, an impedance-transformation circuit electrically connected to the first metallic plate, comprising an isolation capacitor, later referred as blocking capacitor.
• a method of depositing semi-conductive layers in a vacuum comprising the steps of, providing a plasma reactor further including an RF power supply, a vacuum chamber, a reactor chamber, having a reactor impedance, located inside the vacuum chamber, a first and second metallic plate located inside the vacuum chamber; a plasma-discharge region for containing plasma defined between the first and second metallic plates, a feeding element electrically connected to the first metallic plate, and an impedance-transformation circuit electrically connected to the first metallic plate, placing a substrate on the second metallic plate, delivering RF power to the plasma, transforming the reactor impedance to an intermediate impedance with the impedance-transformation circuit, and transforming the intermediate impedance to a feed- through impedance with the feeding element, whereby the feed-through impedance is increased.
• FIGURE 1 is a schematic of a conventional capacitor-coupled, RF-plasma reactor system.
• FIGURE 2 is an equivalent circuit of the reactor system of FIGURE 1.
• FIGURE 3 is a schematic of a capacitor-coupled, RF-plasma reactor system with an impedance-transformation circuit in accordance with the present invention.
• FIGURE 4 is an equivalent circuit of the reactor system of FIGURE 3.
• FIGURE 5 is a graph showing the comparison of the impedance transformation between the conventional circuit of FIGURE 2 and circuit with the impedance-transformation circuit of FIGURE 4.
• FIGURES 3 and 4 a more practical impedance-transformation circuit is shown in the schematic in FIGURE 3 and the electrical equivalent circuit in FIGURE 4. All components described in FIGURES 1 and 2 above that are the same in FIGURES 3 and 4 will not be repeated.
• FIGURE 3 shows a capacitively-coupled, RF-plasma reactor system 40 (hereinafter
• the impedance-transformation circuit 42 includes a transformation circuit feeding element 44 with a grounding shield 46 and a tuneable-blocking capacitor C BT .
• the second feeding element 44 is represented in the equivalent circuit as having parasitic capacitance CT, a lossy element R T , and an low-loss inductor L x .
• the transformation circuit feeding element 44 is located inside the vacuum chamber 18 and is connected to ground via the tuneable-blocking capacitor CB T -
• the transformed RF-plasma reactor system 40 now includes the feeding element 26 and the transformation circuit feeding element 44 both of which are electrically connected to the first metallic plate 22.
• the tuneable-blocking capacitor C BT is located outside the vacuum chamber 18 and can be integrated into the matching network 14, resulting in amended matching network 14' (Fig. 3).
• the tuneable-blocking capacitor CB T can increase the feed-through impedance Re(Zp') thereby decreasing the total RF current Ip' during the deposition process. Further, the tuneable-blocking capacitor CB T can balance the current between the two feeding elements 26, 44 without venting the system.
• I F sqrt[Pp/Re(Z F )]
• the efficiency of the matching network 14 is defined by:
• Qu is the unloaded quality factor of lumped elements and Q L is the loaded quality factor of the lumped elements.
• the optimal balance between I F ' and IT can be adjusted through the tuneable-blocking capacitor CBT and depends on the balance between the power losses of the lossy elements (Rp' +R M ) of the feeding element 26 and matching network 14 and the lossy element Rx of the transformation circuit feeding element 44.
• the total losses in the matching network 14 and the feeding element 26 and transformation circuit feeding element 44 is defined as:
• the loss ratio between the conventional RF-plasma reactor system 10 (no impedance- transformation circuit 42) and the transformed RF-plasma reactor system 40 with the impedance-transformation circuit 42 is:
• the power lost through the lossy elements R M , R F in the conventional RF-plasma reactor system 10 are more than twice as much as the power lost through the lossy elements R M , R F ', R T in the transformed RF-plasma reactor system 40 with the impedance-transformation circuit 42.
• the power delivered to the plasma to maintain the same deposition rate as the conventional RF-plasma reactor system 10 (no impedance- transformation circuit 42) can be reduced.
• a smaller RF power supply can be used to achieve the same deposition rate.
• FIGURE 5 shows a graph that illustrates how the impedance-transformation circuit 42 transforms the feed-through impedance Re(Z F ) to thereby decrease the power lost through the lossy elements.
• the plasma impedance Zp is transformed by a reactor capacitance C R and a reactor inductance LR to a reactor impedance Z R located at the end of the feeding element 26.
• the feeding element 26 then transforms the reactor impedance Z R to a feed-through impedance designated as Z F .
• the plasma impedance Zp is transformed to the reactor impedance ZR just as in the conventional RF-plasma reactor system 10.
• the impedance-transformation circuit 42 transforms the reactor impedance Z R to an intermediate impedance Z R ' .
• the feeding element 26 then transforms the intermediate impedance Z R ' to a feed-through impedance designated as Z F .
• the feed-through impedance Z F has both a higher resistive or real part and a higher inductive reactive or imaginary part than the feed-through impedance ZF. In other words, Re(Zp ) > RC(ZF) and Im(Zp ) > Im(Zp).
• the real part of the feed-through impedance Re(Zp ) is approximately 0.1 to 0.2 ohms whereas the real part of the feed-through impedance Re(Zp) is approximately 0.0 to 0.1 ohms.
• the imaginary part of the feed-through impedance Im(Zp ) is approximately 1 to 5 ohms whereas the imaginary part of the feed-through impedance Im(Zp) is approximately -3 to 1 ohms.
• the impedance-transformation circuit 42 is not intended to compensate for reactive impedance or cancel out phase shifts.
• the more inductive the feed-through impedance Z F however, the less inductance is required in the matching network. As a result, the quality of the matching network can be enhanced even more because the RF power losses are mainly associated with lumped elements such as inductors made from copper.

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Plasma & Fusion (AREA)
• Chemical & Material Sciences (AREA)
• Analytical Chemistry (AREA)
• Electromagnetism (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Chemical Vapour Deposition (AREA)
• Plasma Technology (AREA)
• Multi-Conductor Connections (AREA)

Priority Applications (8)

Applications Claiming Priority (2)

Publications (2)

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ID=36218432

Family Applications (1)

Country Status (10)

Cited By (3)

Families Citing this family (18)

Family Cites Families (13)

• 2005
  • 2005-11-11 DE DE602005022221T patent/DE602005022221D1/de active Active
  • 2005-11-11 EP EP05801054A patent/EP1812949B1/en not_active Not-in-force
  • 2005-11-11 CN CN2005800386843A patent/CN101057310B/zh not_active Expired - Fee Related
  • 2005-11-11 AT AT05801054T patent/ATE473513T1/de not_active IP Right Cessation
  • 2005-11-11 JP JP2007540474A patent/JP5086092B2/ja not_active Expired - Fee Related
  • 2005-11-11 WO PCT/CH2005/000669 patent/WO2006050632A2/en active Application Filing
  • 2005-11-11 KR KR1020077007856A patent/KR101107393B1/ko not_active Expired - Fee Related
  • 2005-11-11 US US11/719,115 patent/US20070252529A1/en not_active Abandoned
  • 2005-11-11 AU AU2005304253A patent/AU2005304253B8/en not_active Ceased
  • 2005-11-14 TW TW094139874A patent/TW200625396A/zh unknown

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